1. Field of the Invention
This invention relates to a method for improving the color of chloro-xylene compositions.
Chloro-xylenes, such as ortho-chloro-para-xylene, are used for various commercial purposes, including the preparation of polymers for films and the like.
2. Description of the Prior Art
It is known in the art to purify liquid organic materials by contact with a suitable adsorbent. The advocacy of a particular purification process through the use of adsorbent materials will depend not only on the adsorbent selected, but on the nature of the liquid to be purified and the impurity to be removed.
U.S. Pat. No. 2,767,226 to Weimer et al discloses the purification of chlorinated benzenes, especially 1,2,4,5-tetrachlorobenzene by removal of dissolved metallic contaminants through the action of an adsorbing agent, such as, a clay, silica gel, calcium hydroxide, magnesium oxide, calcium oxide or calcium carbonate.
U.S. Pat. No. 1,804,458 to Britton discloses the purification of halogenated hydrocarbons such as benzyl chloride, or benzotrichloride by contact with water or a dilute solution of caustic soda, sodium carbonate, or other alkaline compound. After separation of the water the washed product is dried by treatment with a drying agent and/or absorbing agent such as calcium chloride or fillers.
U.S. Pat. No. 2,694,738 to Rucker teaches the treatment of chlorinated hydrocarbons, such as hexachlorocyclohexane, by filtration through an adsorbent, such as, fuller's earth, attapulgus clay, alumina, silica gel or activated carbon, to remove impurities.
Ortho-chloro-para-xylene, in relatively pure form is a substantially colorless liquid typically characterized by color specification of less than about 20 APHA. (APHA denotes a color unit system based on a visual comparison of a sample with standardized aqueous solution of potassium chloro-platinate and cobaltous chloride. The system is described in detail in Standard Methods For The Examination of Water and Waste Water, 15th Ed., American Public Health Association, New York, 1981, pps. 60-63.) Frequently, while in storage or shipment in drums, trailers, tank cars, and the like, ortho-chloro-para-xylenes will develop an undesirable color. The specific cause of discoloration is uncertain. However, since the off-color material is generally unacceptable, it is often necessary to return and re-distill such material. The additional transportation, handling, and re-distillation may add substantially to the overall cost of the chloro-xylene. It will be apparent that a need exists for a simple and inexpensive method to treat off-color material on-site, and thus eliminate the transportation and other costs associated with the return and re-distillation.